Near surface etch selectivity enhancement

Abstract

A method of selectively dry etching exposed substrate material on patterned heterogeneous structures is described. The method includes a plasma process prior to a remote plasma etch. The plasma process may use a biased plasma to treat an untreated substrate portion in a preferred direction to form a treated substrate portion. Subsequently, a remote plasma is formed using a fluorine-containing precursor to etch the treated substrate portion using the plasma effluents. By implementing biased plasma processes, the normally isotropic etch may be transformed into a directional (anisotropic) etch despite the remote nature of the plasma excitation during the etch process.

What is claimed is: 
     
         1 . A method of etching a patterned substrate the method comprising:
 treating the patterned substrate with a local plasma formed from an inert gas, wherein treating the patterned substrate comprises treating an untreated substrate portion to form a treated substrate portion; and wherein the local plasma is formed by applying a local plasma power to excite the local plasma; and   etching the treated substrate portion, wherein etching the treated substrate portion comprises flowing plasma effluents into a substrate processing region housing the patterned substrate after treatment, wherein the plasma effluents are formed by flowing a fluorine-containing precursor into a remote plasma region fluidly coupled to the substrate processing region while forming a remote plasma in the remote plasma region to produce the plasma effluents, wherein forming the remote plasma in the remote plasma region to produce the plasma effluents comprises applying an RF plasma having an RF plasma power to the remote plasma region.   
     
     
         2 . The method of  claim 1  wherein the local plasma comprises argon. 
     
     
         3 . The method of  claim 1  wherein the local plasma power is between about 10 watts and about 500 watts to the substrate processing region. 
     
     
         4 . The method of  claim 1  wherein RF plasma power is between about 300 watts and about 5000 watts to the remote plasma region. 
     
     
         5 . The method of  claim 1  wherein the local plasma is formed by applying a DC bias power such that the local plasma power comprises both an AC portion and a DC portion. 
     
     
         6 . The method of  claim 1  wherein the DC bias power comprises applying a DC bias voltage greater than 400 volts to accelerate inert gas ions toward the patterned substrate. 
     
     
         7 . The method of  claim 1  wherein the plasma effluents enter the substrate processing region through through-holes in a showerhead, and wherein the showerhead separates the remote plasma region from the substrate processing region. 
     
     
         8 . The method of  claim 1  wherein the local plasma consists essentially of inert gases. 
     
     
         9 . The method of  claim 1  wherein the local plasma consists essentially of argon. 
     
     
         10 . A method of etching a patterned substrate the method comprising:
 treating the patterned substrate with a local plasma formed from an inert gas, wherein treating the patterned substrate comprises treating an untreated silicon portion to form a treated silicon portion; and wherein the local plasma is formed by applying a local plasma power;   flowing a fluorine-containing precursor into a remote plasma region fluidly coupled to a substrate processing region while forming a remote plasma in the remote plasma region to produce plasma effluents, wherein forming the remote plasma in the remote plasma region to produce the plasma effluents comprises applying an RF plasma having an RF plasma power to the plasma region; and   etching the treated silicon portion by flowing the plasma effluents into the substrate processing region.   
     
     
         11 . The method of  claim 10  wherein the remote plasma region is devoid of hydrogen during the operation of flowing the fluorine-containing precursor. 
     
     
         12 . The method of  claim 10  wherein the untreated silicon portion is single crystal silicon. 
     
     
         13 . The method of  claim 10  wherein the fluorine-containing precursor comprises at least one of nitrogen trifluoride, carbon tetrafluoride or sulfur hexafluoride. 
     
     
         14 . The method of  claim 10  wherein the local plasma is a capacitively-coupled plasma. 
     
     
         15 . The method of  claim 10  wherein the patterned substrate comprises silicon nitride on both sides of a trench containing the untreated silicon portion before the method begins.